Adjustable grid tracking transmitters and receivers

ABSTRACT

Optical telecommunication receivers and transmitters are described comprising dispersive elements and adjustable beam steering elements that are combined to provide optical grid tracking to adjust with very low power consumption to variations in the optical grid due to various changes, such as temperature fluctuations, age or other environmental or design changes. Thus, high bandwidth transmitters or receivers can be provides with low power consumption and/or low cost designs.

FIELD OF THE INVENTION

The invention relates to optical telecommunication components thatprovide for adjustable optical connections to transducers throughdispersive elements.

BACKGROUND OF THE INVENTION

As telecommunication bandwidths increase, there is a strong demand forlow power consumption, low cost, high bandwidth transmitters andreceivers. To increase bandwidths of optical transmissions between twopoints, wavelength division multiplexing (WDM) can be used in whichinformation is carried on different channels, e.g., N channels, each ata unique wavelength. Adjacent points can be, for example, manykilometers away from each other. The channels can be arranged on awavelength grid, e.g., with uniform spacing in wavelength or frequency,such that the spectral content in each channel does not interfere withadjacent channels. Also, an increase in bandwidth can be achieved usingmodulation at higher data rates. Generally, current technology involvesWDM of 4 to 100 channels and data rates of 2.5 gigabits/second (G), 10G, 25 G or 40 G, although it is expected that these values of channelnumber and modulation rates will evolve over time.

Nodes along a communication network can involve transmitters and orreceivers to interface appropriately with the optical communicationsignals. Optical fibers with multiplexed optical signals generally areused to connect remote points on the network. If the optical channelsare on a wavelength grid or frequency grid, the synchronization of thewavelengths can be expensive and can dissipate considerable power, e.g.to maintain temperature control. Precise control of device productionand operating conditions is typically needed with communication systemsinvolving narrowly spaced wavelength channels to align channelwavelengths with the narrow, passbands of multiplexors/demultiplexors.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to an adjustable opticaltelecommunication transmitter comprising a plurality of light emittingelements that emit optical signals chromatically spaced from each other,a dispersive element and an adjustable beam steering element. Thedispersive element comprises a dispersive structure, a first interfaceproviding a plurality of optical channel paths being optically coupledto the plurality of light emitting elements and to the grating and aconjugate spatially-extended second interface to receive chromaticallycombined signals form the dispersive structure. The adjustable beamsteering element optically can be connected to the first interface or tothe conjugate spatially-extended second interface.

In a further aspect, the invention pertains to an adjustable opticaltelecommunication receiver comprising:

-   -   an input line for coupling to a received optical signal;    -   a dispersive element comprising a dispersive structure, a        spatially-extended input interface for receiving undispersed        optical signals at selectable locations along such interface        with optical signals propagating to the dispersive structure and        an optical output interface for coupling dispersed optical        signals from the dispersive structure to other optical elements;    -   a beam steering element; and    -   a plurality of light receiving elements positioned to receive        the dispersed optical signals from the output interface of the        dispersive element, to generate electrical signals in response        to the dispersed optical signals.        The beam steering element can comprise an actuator and a        controller programmed to dynamically adjust the beam steering        element based on the spectral content of the received optical        signal or other topical parameters, to guide either the        direction of a received optical signal from the input line to a        specific location on the input interface of the planar        dispersive element or the direction of dispersed optical signals        from the output interface to the plurality of light receiving        elements.

In other aspects, the invention pertains to an opticalmultiplexer/demultiplexer comprising a planar dispersive element havinga grating, a first interface for conveying an undispersed optical signalthrough the interface into the grating and a second interface forcoupling dispersed optical signals to other optical elements and a beamsteering element having a first lens and an adjustable reflector withthe first lens positioned between the adjustable reflector and thesecond interface of the planar dispersive element, in which the anglebetween the optical reflector and the second interface can be adjustedto redirect the dispersed optical signal.

In some aspects, the invention pertains to an adjustable, planarmultiplexer/demultiplexer comprising a grating; a plurality of dispersedsignal waveguides interfacing with the grating at a first interface; aspatially-extended second interface to receive chromatically combinedsignals from the grating; and a cantilevered beam steering elementpositioned to receive the chromatically combined signals from thespatially-extended second interface. The cantilevered beam steeringelement can comprise a steerable waveguide operably connected to acantilever structure with electrodes to effectuate adjustment of theposition of the steerable waveguide in response to an electrical signal.

In additional aspects, the invention pertains to a method for providinggrid tracking for an optical transmitter or receiver, the methodcomprising: adjusting a beam steering element configured to receivechromatically combined signal from an optical transmitter or receiver toselect a chromatic grid with a particular center band.

In another aspect, the invention pertains to a method for conveyingmultiple distinct data signals through an optical fiber, said methodcomprising:

-   -   i) transmitting output from a plurality of lasers through a        multiplexing device to form a spectrally combined optical        signal, wherein the output of each laser corresponds to an        independent data signal;    -   ii) transmitting the spectrally-combined optical signal over an        optical fiber; and    -   iii) receiving the spectrally combined optical signal at a        receiver comprising a dispersive element configured to disperse        the combined optical signal into independent optical signals and        a plurality of light receiving elements configured to receive        the independent optical signals that generate an electrical        signal in response to received light,    -   wherein the multiplexing device, the receiver or both comprise a        beam steering element, and wherein the beam steering element is        automatically adjusted by a controller to maintain a signal        intensity at the plurality of light receiving elements        representative of the independent data signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic layout of a transmitter with adjustable gridtracking.

FIG. 2 is a schematic layout of a receiver with adjustable gridtracking.

FIG. 3 is a schematic layout of a transmitter interfaced with a remotereceiver within an optical telecommunication network, in whichtransmitter and receiver have adjustable grid tracking.

FIG. 4 is a top plan view of an embodiment of a transmitter or receiverwith adjustable grid tracking.

FIG. 5A is a top plan view of a De/Mux device with adjustable gridtracking in which the adjustable mirror redirects a chromaticallydispersed signal.

FIG. 5B is a side view of the De/Mux device of FIG. 5A viewed along lineB.

FIG. 5C is a side view of the De/Mux device of FIG. 5A viewed along lineC.

FIG. 6 is a top plan view of a De/Mux with grid tracking based upon aplanar echelle grating.

FIG. 7A is a top plan view of an alternative De/Mux device based upon aplanar echelle grating.

FIG. 7B is a side view of the dispersive element of the De/MUX device ofFIG. 7A.

FIG. 7C is a side view of the planar waveguide structure of the De/MUXdevice of FIG. 7A.

FIG. 8 is a top plan fragmentary view of a planar beam steering elementintegrated into a planar structure incorporating an AWG.

FIG. 9 is a set of plots of measured output from four source channels(1-4) as a function of wavelength and angle of beam steering elementwith lower panels of plots corresponding to slight rotations of theadjustable mirror with a corresponding shift in the wavelengthtransmission.

FIG. 10 is a plot of transmission power as a function of wavelength fora band of four independent optical signals spaced apart by 20 nm.

FIG. 11 is a plot of transmission power as a function of wavelength forthree bands of four independent optical signals each in which theindependent optical signals are spaced apart by 4.5 nm and the bands arespaced apart by 13.5 nm.

FIG. 12 is a top plan view of an embodiment of a transmitter based on anarray of VCSEL light sources, a planar AWG and a free space beamsteering element.

FIG. 13 is a top plan view of a planar AWG with an array of DFB lasersmounted along an edge of the planar AWG to provide optical signals intoa corresponding set of planar waveguides directing the optical signalsinto a slab waveguide of the AWG.

DETAILED DESCRIPTION

An adjustable optical element, e.g., a tunable multiplexor/demultiplexoror a device incorporating a tunable multiplexor/demultiplexor,incorporates a dispersive element and a beam steering element to enablethe tracking of wavelength division multiplexed communication signals. Atunable multiplexor/demultiplexor can be located at a junction between atransmitter or receiver, and an optical transmission waveguide/opticalfiber. This enables the ability to provide for a shifted chromatic grid,which can result from thermal drift, chromatic consistency or otherwavelength adjustment requested from the device. The adjustable deviceinterfaced with the transmitter/receiver can maintain signal integrityon a precision wavelength grid with a beam steering element to directsignals from a dispersive element according to a spatial shift in thesignal, e.g. resulting from temperature changes, such that the devicecan chromatically adapt over a useful range of wavelengths. Thedispersive element can be configured to propagate optical signal, e.g.,a chromatically combined or a chromatically dispersed signal, toward thebeam steering element, and generally small angular redirection of theoptical signal can account for spatial shifts of the optical signal fromthe dispersive element over an appropriate chromatic range. In someembodiments, the tunable feature of the multiplexor/demultiplexor canreplace the use of temperature control, reduce insertion loss despitevariation in manufacturing, and/or enable the efficient use of theoptical spectrum by enabling a narrower wavelength grid.

The dispersive element maps signals at different wavelengths todifferent spatial positions, and the beam steering element allows thewavelengths associated with those spatial positions to be adjusted,enabling tracking of signals as their wavelengths change over a usefulrange. In many dispersive elements, the beam steering element can beplaced to operate on either the dispersed or combined signal. Varioussuitable dispersive elements can be used, such as arrayed waveguidegratings (AWGs) or echelle gratings. Elements of the device generallycan be free space optical elements, planar optical circuit elements orcombinations thereof, and light sources or light receiving elements mayor may not be solid state devices. The dispersive element generallycomprises an input interface and an output interface the guide lightsignals to and from a dispersive structure. The described interfacesgenerally represent an area of location and/or direction with respect tothe dispersive structure and may or may not be associated with aphysical surface. For planar dispersive elements, the respectiveinterfaces can be slab waveguides (which can be called star couplers,star waveguides or other names in the art) or similar optical path thatis not laterally constrained along a confined path.

In some embodiments, a MEMs structure or other mechanical actuatingstructure in combination with a mirror or other reflective/redirectingelement can provide a suitable beam steering element. Generally, smallangular redirection of the optical signal can cover an appropriatewavelength range to provide the desired tunable feature. In general, thewavelengths corresponding to the solid state devices tend to shiftsimilarly to each other in reaction to disturbances such that thewavelength spacing between them is maintained, i.e., tuning as a groupto longer or shorter wavelengths, which allows a single adjustment totrack multiple signals with a small angular redirection.

The combination of the dispersive element and beam steering element forma chromatically adjustable device connecting one or more waveguidesindependently on either end of the device with a dispersed signal on oneend and a combined signal on the other end, with “end” referring to aconceptual and not necessarily a physical location. In some embodiments,the ability to adjust the dispersed signal to adjust for thermal changesprovides the ability to reduce or eliminate a temperature controllerotherwise required on an associated device, such as a thermoelectriccooler on a laser array. Furthermore, the ability to adjust for othercontemporaneous parameters or fabrication parameters influencing thechromatic grid can similarly provide for cost and/or power savings inthe device design and use.

The chromatically dispersed signal generally involves an independentoptical signal corresponding to various data transmission at eachwavelength. The data transmission can correspond to voice, video,documents, combinations thereof or other appropriate data signal(s). Thetransmission of combined optical signals provides for efficient resourceuse and reduction of hardware requirements for transmission of aparticular volume of data. Transmitters convert data signals intocorresponding optical signals, and receivers convert optical signalsinto corresponding electrical signals. A high bandwidth opticaltelecommunication system generally involves precise control to directclosely spaced optical wavelengths through multiplexing and/orde-multiplexing (De/MUX) operations to ensure that dispersive elementsappropriately direct optical wavelengths to their intended locations.Incorporating such precise control can be expensive with respect torequiring careful temperature control and/or matching of opticalelements to achieve desired function. As described herein, dynamiccontrol can be introduced into the device, so that chromatic adjustmentcan be made dynamically to provide for good optical performance with amodest cost design and relatively low power consumption during use.

In an optical communication system, the combination of the dispersiveelement and beam steering element can form a part of a node of apoint-to-point optical telecommunication system connecting one or moresources and/or detectors with respect to the dispersed signals and oneor more waveguides/optical fibers with respect to the combined signal.Wavelengths can then float, i.e. be allowed to change, in someembodiments lowering the costs and power consumption by removing use ofthermoelectric coolers for precise temperature control of associatedcomponents and/or by relaxing manufacturing tolerances for a particularwavelength grid. These components can be used in a chromaticallyfloating, or “unlocked”, high-bandwidth low-cost transmitter orreceiver.

As described herein, control of the beam steering element can bedynamically adjusted to improve the optical signal integrity, generallywith respect to received or transmitted intensity. Thus, to provide forthe use of less expensive design and/or lower power operation withoutsacrificing performance, the optical grid, i.e., wavelength grid orfrequency grid, interfacing with the dispersive element can be allowedto float with respect to spatial, e.g., channel, positioning relative tothe light path or orientation interfacing with the dispersive element.Appropriate adjustment to compensate for the floating optical grid canbe provided by adjustment of the beam steering element, which caninvolve very low power consumption, through the use of a MEMs or otherlow-power-consuming actuator. The dynamic adjustment of the beamsteering element generally is based on a measurement of an opticalsignal or other contemporaneous parameter, such as temperature. Inembodiments of particular interest, the dynamic adjustment generally ismade to account for the floating grid based on a measurement associatedwith the device and not for a random or continuously swept adjustment.The dynamic adjustment can be performed with a suitable beam steeringelement.

A schematic depiction of a dynamically adjustable transmitter is shownin FIG. 1. Transmitter 100 comprises an array of light sources 102, adispersive element 104, beam steering element 106, conveyingwaveguide(s) 108 and control system 110. Flow arrows indicate thegeneral direction of light transmission through transmitter 100. Thearray of light sources 102 generally can comprise an array of lasers,such as a collection of individual semiconductor lasers or a monolithicarray of semiconductor lasers. Dispersive element 104 can convenientlybe a planar optical structure, which can be a component of a planaroptical circuit, although in some embodiments a free space grating canbe used as a dispersive element. Beam steering element 106 can be amirror, other reflector, deflectable waveguide or the like that can bephysically deflected, for example, with the micro-electro-mechanicalactuator (MEMs) or the like or other type of actuator. Beam steeringelement 106 can be conveniently provided as a free space element, butsuitable planar optical beam steering elements are described below.Conveying waveguide(s) can be one or more waveguides that generallycomprise and/or are coupled to optical fiber(s) that can be used toconvey the optical signals to a remote location from the light sources.Control system 110 provides instructions for the adjustment of beamsteering element 106 to provide the desired dynamic control of thetransmitter.

A dynamically adjustable receiver is shown schematically in FIG. 2.Receiver 120 comprises light receiving elements 122, dispersive element124, beam steering element 126, conveying waveguide(s) 128 and controlsystem 130. Flow arrows again are used to indicate the generaltransmission of light through receiver 120. Light receiving elements 122can be appropriate light sensors that measure light impinged onto theelement and provide an electrical signal in response. Dispersive element124, beam steering element 126 and conveying waveguide(s) 128 can beequivalent elements as dispersive element 104, beam steering element 106and conveying waveguide(s) 108 described above with respect totransmitter 100 in FIG. 1. Control system 130 provides instructions forthe adjustment of beam steering element 126 to provide the desireddynamic control of the receiver.

Dynamic control of the receiver provides desirable functionality toreduce cost and power consumption without reducing performance as notedbelow. A receiver with a beam steering element used to scan portions ofa wavelength grid across a detector array is described in U.S. Pat. No.7,952,695 to Crafts et al. (the Crafts patent), entitled “ScanningSpectrometer With Multiple Photodetectors,” incorporated herein byreference. In contrast, the present devices have dynamic control ratherthan a scanning function, which introduces important distinctions withrespect to application. Also, Crafts does not describe structures ormethodology applicable to transmitters. Furthermore, specificembodiments herein can introduce other specific significant distinctionsfrom the structures and/or functions suggested by the Crafts patent.

As noted above, the transmitters and/or receivers generally convey userdata within a telecommunication network, which provides a furtherdistinction from Crafts. A schematic view of a telecommunications linkis shown in FIG. 3. Referring to FIG. 3, a transmitting location 150comprises a plurality of transmitters 152, a dispersive element 154 thatfunctions to multiplex the signals from the transmitters into achromatically combined signal which is directed to a beam steeringelement 156 that directs the optical signal to a waveguide/optical fiber158 that couples the signal to an optical fiber 160 that transmits thesignal to a remote receiving location 170. Remote receiving location 170has a waveguide/optical fiber 172, beam steering element 174, adispersive element 176 that functions to de-multiplex the optical signalinto separate channels and light receiving elements 178 that can provideelectrical signals in response to the separate channels of opticalsignal. Control elements are not shown in the view to simplify thedrawing. The distance between transmitting location 150 and receivinglocation 170 may or may not be large, such as on the kilometer scale.Locations 150, 170 can be nodes along a communication system toredirected signals for further transmission, or they can be end pointsof the communication system in which the de-multiplexed signals areintended for particular end users. In some embodiments, only one of thenodes, i.e., transmitting location 150 or receiving location 170comprises an adjustable beam steering element, for example, if one ofthe locations is designed or controlled to avoid chromatic shifts. Also,a receiving location can comprise an adjustable beam steering elementwhile the transmitting location does not comprise a beam steeringelement where the receiver tracks the transmitter, which can beparticularly suitable if the multiplexor and sources shift at the samerate.

Some specific embodiments are discussed in detail below, but somegeneral features of the basic components of the device are nowsummarized. Transmitters can comprise a plurality of sources thatgenerally emit in different optical channels and are mounted in aspecific physical arrangement to direct the respective optical signalsfor further processing. Sources generally are lasers, such assemiconductor lasers. In some embodiments, the sources can be an arrayof semiconductor lasers mounted on a single chip or the like. Generally,a transmitter comprises at least 4 sources, in other embodiments atleast 10 sources, and in additional embodiments at least 16 sources,although it can be desirable to have a hundred or more sources.

Receivers comprise a plurality of light receiving elements that generateelectrical signals in response to light and are physically arrangedgenerally to receive light in different optical channels. In general,any suitable light receiving elements can be used discretely, diversely,and/or in integrated arrays, including elements such as p-i-nphotodiodes, avalanche photodiodes, MSM photo-detectors, or complexoptical receivers. In some embodiments, an array of solid state lightreceiving elements can be conveniently mounted on a chip. Generally, areceiver comprises at least 4 detectors, in other embodiments at least10 detectors, and in additional embodiments at least 16 detectors,although it can be desirable to have a hundred or more distinctdetectors. A person of ordinary skill in the art will recognize thatadditional ranges of source numbers and/or light receiving elementnumbers within the explicit ranges above are contemplated and are withinthe present disclosure.

In general, any suitable dispersive element can be used to De/MUX theoptical signals, such as prisms, grating or the like. Suitable gratingscan be arrayed waveguide gratings (AWGs), echelle gratings, Bragggratings or the like. While some embodiments can effectively use freespace dispersive elements, in some embodiments it is convenient to usedispersive elements assembled onto planar optical chips or the like. Forexample, a planar AWG is shown in an embodiment of FIG. 4, which isdiscussed further below, and other planar dispersive elements are alsodiscussed. Planar dispersive elements in particular can provide forcompact assembly into a device and a correspondingly smaller footprint,and passive planar devices can be efficiently produced to incorporatedesirable planar dispersive elements.

Also, any reasonable beam steering element can be used, such as amirror, a reflector grid, a deflectable waveguide or fiber or the like.The beam steering element can be a planar structure or a free spaceelement, and there are trade offs with respect to the selection of aplanar or free space element. Examples of both types are provided below.The steering aspect of the optical element can be provided by amechanical element that reorients at least a portion of a reflecting orconveying optical element to redirect the optical path. Generally, asmall reorientation accomplishes the desired redirection of the opticalpath. A small actuator can be desirable from power consumption,precision, device footprint, and other significant perspectives. Smallmechanical actuators are generally referred to asmicro-electro-mechanical or MEMs devices without reference to aparticular design or structure.

Depending on the selected architecture, various planar waveguides and/oroptical fibers can be used to connect elements, and some specificembodiments are described below to provide some examples. Connectors areknown in the art to transition between planar waveguide based devicesand optical transmission fibers. Longer distance optical fibertransmission lines can be used for point to point transmissions andconnected to the devices at the particular node.

A schematic view of an embodiment of an adjustable transmitterincorporating a planar arrayed waveguide grating (AWG) as a dispersiveelement is shown in FIG. 4. This design can be adapted for a receiverthrough the exchange of the light sources with light receiving elementswhere the signal from the light receiving elements 212 can beinterpreted to guide the adjustment the beam steering element instead ofthe tap photoreceiver and the tap is generally not present. In thisembodiment, transmitter 200 comprises a planar dispersing element and afree space beam steering element. Transmitter 200 comprises transmissionwaveguide 202, lenses 204, 206, micro-electro-mechanical systems (MEMs)adjustable mirror 208, AWG 210 and light sources 212. AWG 208 comprisesfirst slab waveguide 212, second slab waveguide 214, an array gratingwaveguides 216 optically connecting first slab waveguide 212 and secondslab waveguide 214 waveguides 218, 220, 222, 224, which are opticallyconnected to second slab waveguide 214 to carry optically dispersedoptical signals. Generally, AWG 210 is formed on a planar optical chipor a planar lightwave circuit (PLC), as described further below. Firstslab waveguide 212 is configured along the edge of the optical chip suchthat free space transmission interfaces with the first slab waveguide212 in contrast with a more conventional structure with light directedinto a planar waveguide guided in both directions. The design with theslab waveguide propagating into free space provides for adjustment ofthe propagation as redirected by the beam steering element. Atemperature sensor can be incorporated into transmitter 200 at variouslocations. Four representative locations are shown in the figure aselements 270 (associated with planar structure 210), 272 (associatedwith light sources), 274 (within the housing (not shown)) and/or 276(associated with planar structure 202). A plurality of thermal sensorscan be incorporated into the system, if desired, in which the values canbe averaged or separately accounted for the in the adjustment of thebeam steering element. A temperature sensor can comprise a thermocouple,thermistor, resistance temperature detector (RTD) or other reasonabledesign.

The components of transmitter 200 are configured such that light fromthe light sources 212 are directed to waveguides 218, 220. 222. 224,which transmit the light to second slab waveguide 214, through arraygrating waveguides 216 and to first slab waveguide 212. A PLC can beconnected to transmitter array using optical fibers and connectors, freespace propagation or through direct attachment of the PLC to the surfaceof the transmitter array using an adhesive or the like. Directconnection of a PLC to a solid state receiver array is described in U.S.Pat. No. 7,272,273 to Yan et al., entitled “Photodetector Couple to aPlanar Waveguide,” incorporated herein by reference. Waveguide 218, 220,222, 224 generally correspond in a one-to-one relationship with elementsof the transmitter. As noted above, the number of transmitter elementscan span noted ranges, and 4 elements are shown in FIG. 4 forconvenience, but the number can be selected as desired within reasonableranges. Some specific embodiments of transmitters are described indetail below.

An AWG may be made as a planar optical structure comprising a substrate,an underclad layer over a surface of the substrate and the AWG over theunderclad layer, optionally with an overclad layer over the opticallytransmitting elements. AWG deigns are known in the art, and can bedesigned for the specific wavelength ranges and channel spacings. Designfeatures for AWGs are described further in U.S. Pat. No. 6,697,552 toMcGreer et al, entitled “Dendritic Taper for an Integrated OpticalWavelength Router,” incorporated herein by reference. To improve opticalcoupling of chromatically dispersed optical signals, second slabwaveguide 214 can incorporate, for example, the dendritic structuredescribed in the '552 patent above or with an optical coupler structureas described copending U.S. patent application Ser. No. 13/679,669 toChen et al., entitled “Wavefront Division Optical Coupler,” incorporatedherein by reference.

To achieve a small device footprint and a low cost, the MEMs structurecan be conveniently used to adjust the mirror angle. One design of aMEMs structure for mirror adjustment is described in U.S. Pat. No.7,016,594 to Godil et al, entitled “Heat Actuated Steering Mount forMaintaining Frequency Alignment in Wavelength Selective Components forOptical Communication,” incorporated herein by reference. Voltagecontrolled MEMs based mirrors are available commercially fromNeoPhotonics Corporation. MEMs devices can operate with sub-milliwattpower consumption.

With the use of a free space beam steering device, it can be desirableto incorporate one or more lenses or the like to control the lightsignal. As shown in FIG. 4, lenses 204, 206 are used to focus the freespace optical signal. In particular, lens 206 focuses the opticalsignals reflected from adjustable mirror 208 toward transmissionwaveguide 202 to decrease loss of optical signal with respect topropagation of the signal in transmission waveguide 202. Lens 204 candiminish the effects of beam spreading of the optical beam when the beampropagates through free space. Appropriately selected lenses or the likecan be used and positioned to decrease dissipation of the opticalsignal. In some embodiments, adjustable mirror 208 can be positionedroughly at one focal length behind lens 206 to reduce optical loss.

Transmission waveguide 202 can be a planar structure or an opticalcoupler connected to an optical fiber. If transmission waveguide 202 isa planar structure, the waveguide can comprise an optical core 240 topropagate light to a coupling element 242 to transfer the optical signalto an optical fiber 244 for longer range transmission. Also, a tap 246can be connected to optical core 240 to direct a small portion of theoptical signal intensity along tap core 248, which directs the tappedsignal to receiver/power meter 250. A reading at receiver/power meter250 can be used to adjust beam steering element 208, for example, toincrease the optical signal.

In use, light sources 212 as well as AWG 210 can be subjected totemperature changes that can cause center wavelength drift of theoptical signal. For example, a light source comprising indium phosphidebased semiconductor laser can exhibit a center wavelength drift rate onthe order of 0.12 nm/° C. A silica based AWG can exhibit a wavelengthdrift on the order of 0.01 nm/° C. Over typical operating temperatureranges of −5° C. to 75° C., the overall change in wavelength can beapproximately 9 nm, resulting in a power loss of greater than 30 dB forwavelengths distributed on a typical grid spacing of 4.5 nm. To helpcompensate for the wavelength drift, MEMs adjustable mirror 188 can bepivoted to shift the center wavelength to compensate for the shift.Control of adjustable mirror 188 is described further below.

Other dispersive elements can be used as noted above. Free spacedispersive elements can include gratings, which can be transmissive(slits) or reflective (spaced apart reflective elements) in design.Suitable gratings include Bragg gratings and echelle gratings. Echellegratings can achieve a compact configuration with a good dispersionthrough use at an angle to the incident light. While higher orderdispersions can overlap in the dispersed light from echelle gratings,for optical telecommunication bands, the range of channels are generallywell dispersed with an echelle grating without necessarily firstinitially dispersing the spectrum with another grating with a higherslit density and approximately normal incidence.

FIG. 5A shows an embodiment of a tunable De/Mux device for incorporationinto a receiver/transmitter. De/MUX device 500 comprises beam steeringdevice 502, AWG 504 and waveguide structure 506. In this embodiment,beam steering device 502 is disposed to receive a chromaticallydispersed signal from AWG 504, in contrast with the embodiment depictedin FIG. 4 in which the beam steering element receives a chromaticallycombined signal from the dispersive element. Beam steering device 502comprises lenses 508, 510, and adjustable mirror 512. The focus of therespective lenses 508, 510 is shown in side views in FIGS. 5B and 5C,which shows positioning to use astigmatism. Adjustable mirror 512 can becoupled to a controller to pivot or otherwise adjust adjustable mirror512, for example, to adjust in response to a particular measurement.

AWG 504 comprises slab waveguides 516, 518 interfaced with an array ofdiffraction waveguides 520 and waveguide 522 for the combined opticalsignal interfaced with slab waveguide 518. Slab waveguide 516 ispositioned to terminate at the edge of the planar device such that lightleaving the slab waveguide propagates into free space toward beamsteering element 502. Slab waveguide 518 couples into waveguide 522 forpropagating the chromatically combined optical signal. Waveguide 522generally is coupled to an optical fiber for longer range transmissionof the chromatically combined signal.

Waveguide structure 506 is shown as a planar optical device with a slabwaveguide 522 positioned along the edge of the waveguide structure 506.Slab waveguide 522 optically couples with waveguides, 524, 526, 528,530, which are positioned to transport chromatically dispersed signalsgenerally with one channel per waveguide. Thus, the number of waveguidescan be designed according to the number of channels. Waveguides 524,526, 528, 530 generally each interface with either an individual lightsource for a transmitter or an individual light receiving element for areceiver. In a receiver, these waveguides can be made multi-mode towiden the wavelength bandwidth of the received light. This can beparticularly useful when there is variation in the wavelength spacingbetween channels that cannot be removed by the tracking function.Multimode waveguides and their use are described further in Amersfoortet al., Electronics Letters 30 (4), pp. 300-302 (February 1994),incorporated herein by reference.

As discussed above with reference to FIG. 4, the pass band of AWG 520can be dependent on the operating temperature and/or other properties oflight, such as polarization state. By incorporating a controller coupledto adjustable mirror 512, light from waveguides 524-530 can be monitoredto detect changes in the center wavelengths of the corresponding datasignals and adjustable mirror 512 can be automatically pivotedaccordingly, to focus desired wavelength ranges on output ports 524-530and diffraction waveguides 520. Thus, adjustable mirror 512 can beautomatically pivoted to tune the wavelengths directed at coupler 516and waveguides 524, 526, 528, 530 of waveguide device 506 and coupler522 and diffraction waveguides 520 of AWG 504. Control of the adjustablemirror is described further below in the context of a suitablecontroller. In some embodiments, it can be desirable for adjustablemirror 512 to be located approximately one focal length from lens 510.Lens 508 of beam steering element 502 is positioned between adjustablemirror 512 and waveguide structure 506. Similarly, lens 510 ispositioned between slab waveguide 516 of AWG 504 and mirror 512. Forsteering of the chromatically dispersed signal the focusing of the freespace propagation can be desirable to reduce signal loss. A shown inFIG. 5, lens 510 can be positioned to image the vertical direction forone facet to the other facet as guided by the free space optics. In asense, the slab waveguide is conceptually divided with the free spaceoptics connecting the sections of slab waveguide to allow a curved focalplane to reduce optical loss.

Another embodiment of an adjustable De/MUX device for integration into atransmitter/receiver based upon an echelle diffraction grating is shownin FIG. 6. De/MUX device 600 comprises beam steering device 602 disposedin the light path between planar diffraction element 604 and waveguide606. The device depicted in FIG. 6 is similar to the correspondingcomponents of the transmitter device in FIG. 4 with the replacement ofAWG 210 with a planar echelle grating based dispersive element.Referring to FIG. 6, beam steering device 602 comprises lenses 608, 610,and adjustable mirror 612, which is analogous with adjustable mirror208, and can be similarly adjusted through pivoting of the mirror.Planar dispersive element 604 comprises planar reflectors 616, 618 andechelle grating 620 positioned to form the light path shown in thefigures between waveguides 622, 624, 626, 628 and edge 630. The opticalpath through planar dispersive element 604 is located along a generallylaterally unconfined core layer except for constrained waveguides 622,624, 626, 628. Reflectors 616, 618 can be formed with a metal ordielectric coating or by utilizing total-internal-reflection. One ormore of waveguides 622, 624, 626, 628 can have a bend (e.g. an s-bend)to position the waveguides along the edge of the planar structure in amore spaced configuration to facilitate connection to optical fiber orother optical element. Reflectors 616, 618 can have a concave reflectingsurface to focus light reflecting from the elements, which can counterspreading of the beam during transmission through the planar element.The relative orientation of the surface of the diffraction grating canbe selected such that a selected diffraction order is scattered alongthe optical path between reflectors 616, 618. A free space echellegrating for Multiplexing/Demulitplexing is described U.S. Pat. No.6,647,182 to Sappey et al. (the '182 patent), entitled “Echelle GratingDense Wavelength Division Multiplexer/Demultiplexer,” incorporatedherein by reference, and such a grating can be adapted for the currentdevices as a free space grating or for the design of a planar grating asdescribed with respect to FIG. 6.

As described above, adjustable mirror 612 can be automatically pivotedto tune the wavelengths directed at interface 630 and waveguide 632 ofwaveguide device 606. Pivoting of adjustable mirror 612 can focusdesired wavelengths to tune the wavelength grid of echelle grating 604in response to detected changes in center wavelength in one or more ofwaveguides 622-628.

In some embodiments, an echelle grating-based tunable De/MUX device canbe made more physically compact by designing a planar refractive elementcomprising a curved grating that can simultaneously focus and dispersethe optical signal. FIG. 7A shows an embodiment of a planar dispersiveelement with a curved grating. The De/MUX device of FIG. 7A is similarto the De/MUX elements shown in FIG. 4 with the AWG replaced by theplanar dispersive element based on the curved grating. De/MUX device 700comprises planar dispersive element 702, beam steering element 704 andtransmission waveguide 706. Dispersive element 702 comprises curvedgrating 712 disposed between waveguides 714, 716, 718, 720, reflector722 and interface 724. A side view of dispersive element 702 is shown inFIG. 7B. Curved grating 712 comprises a reflective, curved grating witha design of an echelle grating. The '182 patent describes a free spacecurved echelle grating for corresponding use as a free space element.Beam steering device 704 comprises lenses 726, 728, and adjustablemirror 729. The focus of the respective lenses 726, 728 is shown in sideviews in FIGS. 7B and 7C. Transmission waveguide 706 is a planarstructure that comprises optical core 731. Optical core 731 can beconnected to a tap as shown in FIG. 4 for transmission waveguide 202.

Planar dispersive element 702 is advantageous in that the combinedreflector/grating allows for a more compact device. However, because thefocusing element and echelle grating are combined, the blaze (i.e. theselection wavelength range placed onto target locations along theoptical path) and angle of incidence of light at interface 724 andwaveguides 714-720 cannot be simultaneously adjusted because of loss ofoptical degrees of freedom due to combination of the focusing elementand echelle grating. Both practical constraints in design of opticaltransmission along interface 724 and corresponding focusing at theinterface can introduce some optical loss. However, increasing thedistance between the focal point at interface 724 and the focal point atwaveguides 714-720 can reduce the optical loss.

As noted above, the beam steering component can be a planar opticalcomponent rather than a free space component. An embodiment of a beamsteering element integrated into the planar structure also comprising anAWG is shown in FIG. 8 in a fragmentary view of the entire planarcomponent. Referring to FIG. 8, planar structure 730 comprises an arrayof waveguides 732, a slab waveguide 734 adjacent planar beam steeringelement 736, waveguide 738, connector 740 and optical fiber 742. Planarbeam steering element 736 comprises a cantilevered waveguide 750, a combdrive 752 and electrodes 754, 756, 758. Comb drive 752 provides for theflexing of the cantilevered waveguide one way or the other through theapplication of voltage to waveguide electrode 754 and one or the otherof the edge electrodes 756, 758. Electrodes can be formed by depositedmetal, for example, on the sidewalls and top by sputtering or othersuitable deposition approach. The shaded portions of the comb drive aregenerally etched downward, and undercutting can release the cantileveredwaveguide and comb drive components. The comb drive operates to move thewaveguide through electrostatic actuation. A design of a planarcantilever based element interfaced with waveguides to form a switch isdescribed in U.S. Pat. No. 5,078,514 to Valette et al., entitled “Switchand System for Switching Integrated Optical Multichannels and SwitchProduction Method,” incorporated herein by reference. The formation of acomb drive for an optical switch is described in detail in U.S. Pat. No.7,709,354 to Stowe et al., entitled Optical Steering Element andMethod,” incorporated herein by reference, and the processing can beadapted for the comb drive configuration shown in FIG. 8.

As noted in the context of FIGS. 1 and 2, a control system is used toadjust the adjustable mirror based on a contemporaneous measuredparameter. The control system can comprise any suitable hardwaredevices, such as an analog to digital converter to interface with asensor, a processor such as a dedicated integrated circuit and/or ageneral purpose microprocessor programmed for control of the MEMs devicefor adjustment of the beam steering element, a digital to analogconverter to send a signal to the MEMs device, appropriate one or moreamplifiers, wire or wireless communication lines or the like. Adjustmentof pivoting mirrors with a MEMs structure in an opticaltelecommunications device is described further in U.S. Pat. No.6,914,916 to Pezeshki et al., entitled “Tunable Controlled Laser Array,”incorporated herein by reference.

For a receiver, the measurements on one or more of the light receivingelements can be correlated with the beam steering adjustment to get agreater measured signal, for example. Thus, a feedback loop can be usedfor example periodically, such as every minute or every hour, to adjustthe mirror to increase received signal. For a transmitter, a tap can beused, such as shown in FIG. 4, to measure the output from thetransmitter to provide a parameter to provide for adjustment of theadjustable mirror to maintain a desired high output. For example,drifting of signal wavelengths can occur with age, and the adjustablemirror can be used to compensate for changes with age.

In some embodiments, the adjustment can be performed to adjust fortemperature fluctuations. Temperature fluctuations can influence theperformance of light sources, such as lasers, and dispersing elements,such as AWGs or other gratings. The changes induced by a temperaturechange can be adjusted by the direct measurements of the optical signalsas described in the previous paragraph. In additional or alternativeembodiments, a temperature sensor can be used, as shown in FIG. 4. Basedon either design parameters or measurements of device performancemeasured for the device at known temperatures, an algorithm or a lookuptable can be generated and used to correlate appropriate mirroradjustment based on temperature measured with one or more temperaturesensors.

AWGs have been previously designed with passive temperature adjustmentcapabilities. Desirable embodiments of temperature compensating AWGs arefound in published U.S. patent application 2012/0308176 to McGinnis,entitled “Thermally Compensated Arrayed Waveguide Grating Assemblies,”incorporated herein by reference. The present approach to thermalcompensation provides greater flexibility with respect to the previousapproaches with respect to temperature compensation. In particular, thepresent approaches can provide for thermal changes in additionalcomponents of the system in addition to the dispersive elements, foradditional changes to the operation of the device over time, otherenvironmental changes and for design changes for the integration of thedevice into a telecommunication system. Thus, the current design canprovide significant desirable functionality in comparison with thealready useful designs in the McGinnis reference above.

Due to the tunability of chromatically dispersed light from thedispersive element, the De/MUX apparatuses described herein supportcloser spacing of uncontrolled wavelengths and can provide for more datachannels in the same wavelength span relative to alternative De/MUXapparatuses. To predict the improved bandwidth, simulations of atransmitter as shown in FIG. 4 were performed using the commerciallyavailable BeamPROP™ software (Synopsis, Inc.; Mountain View, Calif.).AWG 210 was simulated as a silica based AWG having a 1310 nm centeredLR4 grid with a spacing of 4.5 nm. The effect of the MEMs based beamsteering component was simulated by spatially displacing the inputwaveguide launch of first slab waveguide 212 and plotting the outputspectrum for the four light sources 218-224. FIG. 9 is a composite ofgraphs showing the simulated power output versus simulated frequency oflight sources 218-224 as adjustable mirror 208 is rotated. The top panelcorresponds to a center wavelength launch and successively lower panelscorrespond to off-center wavelength launches, with increasing rotationangle of adjustable mirror 208. As shown in 9, drift in the centerwavelength of the data channels (1-4) can be tracked by measuring theoutput power in output channels associated with waveguides 218-224.Since many effects can cause the grid wavelength to shift while the gridspacing remains relatively constant, using total power coupled to thewaveguide can be an effective signal to use to adjust the adjustablemirror. While the simulation has been described in the context of atransmitter with the dispersive element operating as a multiplexer,however, the simulation results also predict the chromatic dispersingperformance since the relevant portions of the apparatus are symmetric.

As a specific example of a wavelength grid that can take advantage ofthe tracking adjustable devices described herein, FIG. 10 shows anexample of a standard colorless grid used in IEEE802.3ba 40GBASE-LR-4standard. Transmission is shown with parabolic curves. The channelspacing is fairly large, 20 nm, since typically the multiplexor anddemultiplexor wavelengths shift approximately 10 times less than thelaser wavelengths. As temperature changes correspondingly change thelaser wavelengths, shown by solid vertical lines at room temperature,shift as represented by dashed vertical lines, which are generally atlonger wavelengths for increasing temperatures. A corresponding shift toshorter wavelengths would take place for decreasing temperatures. Inorder to keep the transmission high and cross talk between the channelslow, the channel spacing is set to be fairly large, 20 nm.

In contrast, FIG. 11 show how density can be increased when trackingmulitplexors and de-multiplexors are used as described herein. Thus, agrid of 4.5 nm can be used based on transceiver components similar tostandard IEEE802.3ba 100GBASE-LR4 components, with essentially the samedevice design parameters other than the tracking function. Since all ofthe wavelengths for each transmitter or receiver section go up and downapproximately together, it is possible for the channel spacing to bereduced while maintaining good transmission and low cross talk betweenadjacent channels. Filter passbands shift with incoming signals tomaintain good optical performance. It can be seen from FIGS. 10 and 11that it can be possible to fit 3 independent bands of 4 channels in thesame spectrum that have fit only 1 band before, even if each band wasseparated by a 13.5 nm guard band and allowed to independently shift inwavelength. Transceivers for operation based on the IEEE standards for40 Gb/s and 100 Gb/s operation are described generally in Cole et al.,“Photonic Integration for High-Volume, Low-Cost Applications,” IEEECommunications Magazine, S16-S22, March 2009, incorporated herein byreference.

Additionally, a tracking receiver can be used with the 20-nm spacedtransmitters based on the IEEE802.3ba 100GBASE-LR4 standard or with afloating transmitter proposed here, reducing the number of receivertypes that would need to be provided. If a cyclic AWG was used in thetracking receiver, then the same part can be used for the additionalbands at other wavelengths proposed in FIG. 11. The function of an AWGas a cyclic multiplexer is described in Dragone et al., “IntegratedOptics N×N Multiplexer on Silicon,” IEEE Photonics technology Letters3(10), 896-899 (October 1991), incorporated herein by reference.

The materials for forming the PLC can be deposited on a substrate usingCVD, variations thereof, flame hydrolysis or other appropriatedeposition approach. Suitable substrates include, for example, materialswith appropriate tolerance of higher processing temperatures, such assilicon, ceramics, such as silica or alumina, or the like. In someembodiments, suitable silicon dioxide precursors can be introduced, anda silica glass can be doped to provide a desired index of refraction andprocessing properties. The patterning can be performed withphotolithography or other suitable patterning technique. For example,the formation of a silica glass doped with Ge, P and B based on plasmaenhanced CVD (PECVD) for use as a top cladding layer for a PLC isdescribed in U.S. Pat. No. 7,160,746 to Zhong et al., entitled “GEBPSGTop Clad for a Planar Lightwave Circuit,” incorporated herein byreference. Similarly, the formation of a core for the optical planarwaveguides is described, for example, in U.S. Pat. No. 6,615,615 toZhong et al., entitled “GEPSG Core for a Planar Lightwave Circuit,”incorporated herein by reference. The parameters for formation of anappropriate waveguide array are known in the art.

A specific embodiment of a transmitter incorporating the tuning functiondescribed herein is shown in FIG. 12. Transmitter 800 comprises an arrayof VCSEL (vertical cavity surface emitting laser) sources 802, planardispersive element 804, beam steering element 806, planar lightconnector 808 and control system 810. Array of VCSEL sources 802comprise's 810 a to 810 x, where x is the number of VCSEL lasers. TheVCSELs can provide a low power consumption source that is suitable fortelecommunications operation.

In some embodiments, the VCSEL are selected to be at periodic or spacedapart wavelengths on a grid. A multi-wavelength VCSEL array can be madeby introducing growth non-uniformly, for example, directly or withselective area growth, which allows multiple arrays to be manufacturedon each wafer. Direct formation of suitable VCSEL arrays is described inChang-Hasnain et al., IEEE Journal of Quantum Elect., V. 27, No. 6, p1368 (1991) and Maeda et al., IEEE Photonics Technology Letters, V. 3,No. 10 p, 863 (1991), both of which are incorporated herein byreference. In additional or alternative embodiments, VCSEL arrays can beused based on high contrast gratings, as described in Mateus et al.,IEEE Photonics Technology Letters, Vol., 16, No. 2, pp 518-520 (2004),incorporated herein by reference.

Planar dispersive element 804 comprises a planar lightwave circuit (PLC)with waveguides 820 a-820 x, first slab waveguide 822, waveguide array824 and second slab waveguide 826. Planar dispersive element 804combines the VCSEL wavelengths into one fiber. VCSEL are mounted alongthe edge of planar dispersive element 804 with a VCSEL element alignedwith a corresponding waveguide 820. Waveguides 820 transport light tofirst slab waveguide 822 at one end of waveguide array 824. Second slabwaveguide 826 is at the other end of waveguide array 824 from first slabwaveguide 822 and located at an edge of the PLC such that light fromsecond slab waveguide 826 propagates into free space.

Beam steering element 806 comprises first lens 840, adjustable mirror842, optical isolator 844 and second lens 846. First lens 842 is locatedabout 1 focal length from planar dispersive element 804. Adjustablemirror 842 comprises mirror element 848 and mirror actuator 850. Mirrorelement 848 is positioned to reflect light from first lens 840 tooptical isolator 844, which inhibits reflection of light back toward theVCSEL. Lens 846 receives light from optical isolator 844 and ispositioned about a focal length from planar light connector 808.

Planar light connector 808 comprises transmission waveguide 860, tapconnector 862, tap waveguide 864, receiver/light meter 866 and opticalfiber connector 868. As shown in FIG. 10, optical fiber 870 is connectedto optical fiber connector 868. Receiver/light meter 866 is connected tocontrol system 810 through a wired or wireless connection to send asignal related to the amount of light received at receiver/light meter866. Control system 810 is also connected to mirror actuator 860.Control system 810 can be programmed to adjust mirror actuator 860 tomaintain a high light intensity at receiver/light meter 866 indicating adesired high light intensity in optical fiber 870. Adjustment of mirror848 can compensate for drop in light intensity due to temperaturechanges, aging of the system or other fluctuating parameter influencingthe light transmission.

A similar structure can be correspondingly assembled using an arraydistributed feedback (DFB) lasers as a substitute for VCSEL lasers.Arrays of DFB lasers for optical telecommunication operation aredescribed further in U.S. Pat. No. 6,914,916 to Pezeshki et al.,Entitled “Tunable Controlled Laser Array,” incorporated herein byreference. An array of DFB lasers can be mounted along an edge of adispersive element, as shown in FIG. 13, to replace the array of VCSELsources 802 and planar dispersive element 804 of FIG. 12. DFB laserarrays can be monolithically integrated onto a single semiconductor chipor fabricated with one laser per semiconductor chip. Monolithicintegration can reduce material cost and size. Fabrication of one laserper semiconductor chip can allow individual laser screening for improvedyield.

Referring to FIG. 13, array of DFB lasers 882 are mounted on planardispersive element 884. Array of DFB lasers 882 comprises 886 a to 886x, where x is the number of DFB lasers. Planar dispersive element 884comprises a planar lightwave circuit (PLC) with waveguides 890 a-890 x,first slab waveguide 892, waveguide array 894 and second slab waveguide896. Planar dispersive element 884 combines the DFB wavelengths into onefiber. DFB lasers are mounted along the edge of planar dispersiveelement 884 with a DFB laser element aligned with a correspondingwaveguide 890. Waveguides 890 transport light to first slab waveguide892 at one end of waveguide array 894. Second slab waveguide 896 is atthe other end of waveguide array 894 from first slab waveguide 892 andlocated at an edge of the PLC such that light from second slab waveguide896 propagates into free space. Planar dispersive element 884 can beinterfaced then with a beam steering element, planar light connector andcontrol system, which can be similar to the beam steering element 806,planar light connector 808 and control system 810 of FIG. 12. DFB laserstypically produce higher maximum power than VCSELs. VCSELs generally canbe high speed and efficient at lower powers than DFBs.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What is claimed is:
 1. An adjustable optical telecommunicationtransmitter comprising: a plurality of light emitting elements that emitoptical signals chromatically spaced from each other; a dispersiveelement comprising a dispersive structure, a first interface providing aplurality of optical channel paths being optically coupled to theplurality of light emitting elements and to the grating, and a conjugatespatially-extended second interface to receive chromatically combinedsignals from the dispersive structure; and an adjustable beam steeringelement optically connected to the first interface or to the conjugatespatially-extended second interface.
 2. The adjustable opticaltelecommunication transmitter of claim 1 wherein the adjustable beamsteering element is optically connected to the spatially-extended secondinterface and comprises an actuator and a controller programmed toadjust the beam steering element to adjust the direction to guide thechromatically combined optical signal to a transmission waveguide. 3.The adjustable optical telecommunication transmitter of claim 1 whereinthe dispersive element is planar and the dispersive structure comprisesan arrayed waveguide grating.
 4. The adjustable opticaltelecommunication transmitter of claim 1 wherein the dispersivestructure comprises an echelle grating.
 5. The adjustable opticaltelecommunication transmitter of claim 1 wherein the plurality of lightemitting elements comprise an array of lasers.
 6. The adjustable opticaltelecommunication transmitter of claim 1 wherein the plurality of lightemitting elements comprises a series of individual lasers selected forwavelength and directly attached to the first interface of thedispersive element.
 7. The adjustable optical telecommunicationtransmitter of claim 1 wherein the beam steering element comprises amirror and a MEMS device configured to adjust the angle of the mirrorrelative to the dispersive element.
 8. The adjustable opticaltelecommunication transmitter of claim 1 wherein the dispersivestructure is planar and wherein the beam steering device comprises aplanar cantilever structure integrated into a planar structurecomprising the dispersive element.
 9. The optical telecommunicationtransmitter of claim 8 wherein the planar cantilever structure includesa waveguide to guide an optical signal.
 10. The opticaltelecommunication transmitter of claim 8 wherein the planar cantileverstructure is moved through electrostatic actuation.
 11. The adjustableoptical telecommunication transmitter of claim 1 wherein the pluralityof light emitting elements comprises an array of lasers and the beamsteering element comprises a MEMS device, and further comprising afocusing element to focus light from the dispersive element to atransmission waveguide by way of the MEMS device wherein the angularadjustment of the MEMS device provides for chromatic grid selection. 12.The adjustable optical telecommunication transmitter of claim 1 whereinthe dispersive element is a planar optical element and thespatially-extended interface comprises a slab waveguide section.
 13. Theadjustable optical telecommunications transmitter of claim 1 wherein theadjustable beam steering element is optically connected to the firstinterface.
 14. An adjustable optical telecommunication receivercomprising: an input line for coupling to a received optical signal; adispersive element comprising a dispersive structure, aspatially-extended input interface for receiving undispersed opticalsignals at selectable locations along such interface with the opticalsignals propagating to the dispersive structure and an optical outputinterface for coupling dispersed optical signals from the dispersivestructure to other optical elements; a beam steering element; and aplurality of light receiving elements positioned to receive thedispersed optical signals from the output interface of the dispersiveelement, to generate electrical signals in response to the dispersedoptical signals, wherein the beam steering element comprises an actuatorand a controller programmed to dynamically adjust the beam steeringelement based on the spectral content of the received optical signal orother topical parameters, to guide either the direction of a receivedoptical signal from the input line to a specific location on the inputinterface of the planar dispersive element or the direction of dispersedoptical signals from the output interface to the plurality of lightreceiving elements.
 15. The adjustable optical telecommunicationreceiver of claim 14 wherein the dispersive element is planar, thedispersive structure comprises one of an arrayed waveguide grating, anechelle grating, or a planar Bragg grating and the spatially-extendedinput interface comprises a slab waveguide.
 16. The adjustabletelecommunications receiver of claim 15 wherein the beam steeringelement is located between an input transmission waveguide configuredfor carrying a chromatically combined optical signal and the inputinterface.
 17. The adjustable optical telecommunication receiver ofclaim 14 wherein the beam steering element comprises a mirror and a MEMsdevice configured to adjust the angle of the mirror.
 18. The adjustableoptical telecommunication receiver of claim 14 wherein the controller isprogrammed to adjust the beam steering element to optimize receivedsignal power at one or more light receiving elements.
 19. The adjustableoptical telecommunication receiver of claim 14 wherein the controller isprogrammed to adjust the beam steering element based on an inputparameter.
 20. The adjustable optical telecommunication receiver ofclaim 18 wherein the input parameter relates to a wavelength range. 21.The adjustable optical telecommunication receiver of claim 14 whereinthe topical parameters are correlated with temperature.
 22. Theadjustable optical telecommunication receiver of claim 14 wherein thedispersive element is planar, wherein the dispersive structure comprisesan AWG and the beam steering element comprises a MEMS device and whereinthe beam steering element guides the direction of a received opticalsignal from the input line to a specific location on the input interfaceof the planar dispersive element.
 23. The adjustable opticaltelecommunication receiver of claim 14 wherein the beam steeringelements guides the direction of dispersed optical signals from theoutput interface to the plurality of light receiving elements.
 24. Anoptical multiplexer/demultiplexer comprising: a planar dispersiveelement having a grating, a first interface for conveying an undispersedoptical signal through the interface into the grating and a secondinterface for coupling dispersed optical signals from the grating toother optical elements; a beam steering element having a first lens andan adjustable reflector with the first lens positioned between theadjustable reflector and the second interface of the planar dispersiveelement, wherein the angle between the optical reflector and the secondinterface can be adjusted to redirect the dispersed optical signal. 25.The optical multiplexer/demultiplexer of claim 24 wherein the lens isabout a focal length from the second interface.
 26. The opticalmultiplexer/demultiplexer of claim 24 wherein the grating comprises anarrayed waveguide grating and the first interface and the secondinterface are slab waveguides.
 27. The optical multiplexer/demultiplexerof claim 24 wherein the grating comprises an echelle grating.
 28. Theoptical multiplexer/demultiplexer of claim 24 beam steering elementcomprises a mirror and a MEMs actuator configured to adjust the positionof the mirror.
 29. An adjustable, planar multiplexer/demultiplexercomprising: a grating; a plurality of dispersed signal waveguidesinterfacing with the grating at a first interface; a spatially-extendedsecond interface to receive chromatically combined signals from thegrating; and a cantilevered beam steering element positioned to receivethe chromatically combined signals from spatially-extended secondinterface and comprising a steerable waveguide operably connected to acantilever structure with electrodes to effectuate adjustment of theposition of the steerable waveguide in response to an electrical signal.30. The adjustable, planar multiplexer/demultiplexer of claim 29 whereinthe grating is an arrayed waveguide grating or an echelle grating.
 31. Amethod for providing grid tracking for an optical transmitter orreceiver, the method comprising: adjusting a beam steering elementconfigured to receive chromatically combined signal from an opticaltransmitter or receiver to select a chromatic grid with a particularcenter band.
 32. A method for conveying multiple distinct data signalsthrough an optical fiber, said method comprising: i) transmitting outputfrom a plurality of lasers through a multiplexing device to form aspectrally combined optical signal, wherein the output of each lasercorresponds to an independent data signal; ii) transmitting thespectrally-combined optical signal over an optical fiber; and iii)receiving the spectrally combined optical signal at a receivercomprising a dispersive element configured to disperse the combinedoptical signal into independent optical signals and a plurality of lightreceiving elements configured to receive the independent optical signalsthat generate an electrical signal in response to received light,wherein the multiplexing device, the receiver or both comprise a beamsteering element, and wherein the beam steering element is automaticallyadjusted by a controller to maintain a signal intensity at the pluralityof light receiving elements representative of the independent datasignals.
 33. The method of claim 32 wherein the lasers comprise verticalcavity surface emitting lasers or distributed feedback lasers andwherein the multiplexing device comprises an AWG.
 34. The method ofclaim 33 wherein another beam steering element is located between theAWG and the optical fiber.
 35. The method of claim 32 wherein theoptical fiber connects remote locations.
 36. The method of claim 32wherein the beam steering element comprises a MEMS device and a pivotingmirror operably connected to the MEMS device to provide for adjustmentof the mirror orientation.